Inflatable seal

ABSTRACT

There is provided an inflatable peripheral seal which is characterized by a closed loop gas-impervious body of an elastomeric material formed from an extruded section and joined at its ends and having oppositely disposed inner and outer peripheral sealing surfaces. The loop contains at least one interiorly disposed continuous chamber defined in part by a flexible wall which is movable between a first position and a second position in response to fluid pressure. The wall is stable in the first position when the pressure differential across the wall is below a predetermined value. The joint between the ends of the extruded section is free of tensile stresses both when the seal is inflated and deflated. Further, the joint can be made after the seal is positioned around a shaft so that the seal can be installed without moving the seal over the ends of such shaft.

United States Patent Satterthwaite et al.

[ 1 Sept. 5, 1972 [54] INFLATABLE SEAL [72] Inventors: James GlennSatterthwaite, 5001 Dogwood Trail, Portsmouth, Va. 23703; James B. Macy,Jr., 107 Holly Lane, Morehead City, NC. 28557 22 Filed: Feb. 3, 1970 21App1.No.: 8,278

[52] US. Cl ..277/34 [51] Int. Cl. ..Fl6l 33/16, F16j 15/46 [58] Fieldof Search ..277/34, 34.3, 34.6, 226

[56] References Cited UNITED STATES PATENTS 2,943,874 7/1960 Valdi etal. ..277/34.3 2,841,422 7/1958 Badger ..277/34 3,178,779 4/1965 Clarket al. ..277/34 X 2,822,192 2/ 1958 Beatty ....277/34 X PrimaryExaminerSamuel B. Rothberg Att0rneyMcNenny, Farrington, Pearne andGordon [5 7 ABSTRACT There is provided an inflatable peripheral sealwhich is characterized by a closed loop gas-impervious body of anelastomeric material formed from an extruded section and joined at itsends and having oppositely disposed inner and outer peripheral sealingsurfaces. The loop contains at least one interiorly disposed continuouschamber defined in part by a flexible wall which is movable between afirst position and a second position in response to fluid pressure. Thewall is stable in the first position when the pressure differentialacross the wall is below a predetermined value. The joint between theends of the extruded section is free of tensile stresses both when theseal is inflated and deflated. Further, the joint can be made after theseal is positioned around a shaft so that the seal can be installedwithout moving the seal over the ends of such shaft.

20 Claims, 8 Drawing Figures INFLATABLE SEAL BACKGROUND OF THE INVENTIONThe present invention relates generally to peripheral seals and moreparticularly to inflatable ring type seals. These inflatable seals areof particular utility in an annulus between tubular bodies subject tovarious conditions of rotational relative movement, and axial relativemovement. Thus, these seals have wide utility for a variety ofstructures including, for example, shaft seals for marine propellershafts extending through the wall of a vessel; internal sealing meansfor pipe; and pipe or shaft couplers of various kinds, e.g., rigid orflexible, stationary or rotatable, etc. It will be understood, how ever,that the principals of this invention may be employed in otherapplications.

The invention will be discussed for convenience with more particularreference to marine installations. The propeller shaft as it passesthrough the hull of a marine vessel may be supported by a waterlubricated rubber bearing or the like. An example of such a bearing isdescribed in U.S. Pat. No. 3,407,779. When such bearing is located inthe stern tube, a shaft seal is provided inboard of the bearing toprevent water from entering the hull. In addition to providing a seal toprevent the flow of sea water into the hull, this sealing assembly isalso conveniently utilized for the force admission of lubricating fluid,e.g., water, to the stern tube or shaft bearing. Vessels commonlyencountering poluted waters or harbors or inland waterways sometimesutilize filtered water applied to the bearing from inside the vesselwhich flows through the shaft bearing in an outboard direction underpositive pressure.

These prior structures have often utilized a fibrous packing bodycompressible by a packing gland into sealing relation with the shaft. Toprevent excessive wear and to provide cooling, it is customary to adjustthe packing so that it is sufficiently loose to permit a controlledamount of water to flow in an inboard direction into the hull. Water isnot a preferred lubricant for fibrous packing members in confrontingrelation with a relatively moving metal shaft. Therefore, wear tends tooccur.

When it became necessary to replace the packing, and in order to avoidremoval of the vessel from the water, a temporary, selectively operablesealing means in the form of an inflatable ring or pneumatic seal hasbeen provided in the shaft seal apparatus outboard of the fibrouspacking member or members. When inflated, these sealing means distendedinwardly and peripherally contacted the shaft with a force sufficient towithstand the hydrostatic pressure of water attemping to flow into thehull along the shaft, thereby permitting replacement of the fibrouspacking member or members while the vessel remained in the water.Examples of such seals are disclosed in the US. Pat. Nos. 2,648,554;2,946,608, and 3,121,570.

In the past, difiiculty has been encountered with seals of this generaltype since they have tended to wear and fail. The wearing failure ofsuch seals has tended to occur from two causes. First, when the seal wasinflated, the rubber forming the seal contact surface tended topermanently deform after becoming distended thus causing contact to bemaintained between portions of the seal contact surface and the shafteven after the seal was deflated. Such contact over a period of timecaused the seal to wear thin with ultimate failure. Further, thedeflating or exhausting of the pressurizing fluid from the interior ofthe seal after it has been inflated is often not complete and a smallresidual pressure remains in the seal. When this occurs, the permanentdeformation is augmented and seal wear becomes greatly accelerated.

Generally in the past, the inflatable seal has been operated only whenit was necessary to repair or replace the packing. However, in manyinstances, the inflatable seal is presently operated whenever the vesselis tied up and is not under power for a period of time. For example, inmany rivers and harbors, polution control regulations have beenestablished restricting the pumping of bilges and restricting thedischarging of other forms of waste. Since the typical stuffing boxpermits a continuous flow of water at a controlled rate through thegland area, there is a tendency for water to accumulate in the bilges orelsewhere in the vessel which water must be pumped out at intervals. Inorder to prevent the leakage of water in through the stuffing box whenthe shaft is not rotating, the practice has therefore been establishedin many instances to inflate the seal to positively prevent any furtherflow of water into the vessel along the shaft whenever the shaft is notin operation. Consequently, the shafts seals are inflated far more oftenthan in the past where they were used only to permit repair orreplacement of the packing. Consequently, the likelihood of damage tothe seal resulting from permanent deformation or from failure tocompletely deflate the seal is greatly increase.

SUMMARY OF THE INVENTION In our copending application, Ser. No. 791,082,filed Jan. 14, 1969, the disclosure of which is incorporated herein byreference thereto, we have discussed an improved inflatable seal havingimproved nonwear characteristics thereby reducing the necessity forreplacement. Insofar as the embodiment of the present invention inmarine propeller shaft seals is concerned, the present inventionprovides a novel and improved one piece seal to provide access toinstallation of the ring seal around the shaft without removing theshaft and without requiring a split housing.

Also, the improved seal can be pressurized under controlled conditions,in relation to the environmental hydrostatic pressure, wherein the sealcontact surface engages a rotating journal surface with sufficientpressure differential to serve effectively as a running seal.Lubrication is adequately provided by the boundary layer of waterwetting the journal surface under the seal as a result of capillaryaction. Under such controlled conditions, the seal can be used attheends of outboard bearings around a rotating or stationary shaft, to seala desired lubricant within the system, while sealing the environmentalwaters out.

In another embodiment of the present invention, instead of providing aseal about the outside diameter of a shaft, a seal is provided on theinside diameter of a pipe, for example. The structures of the presentinvention are also adapted for use in providing a seal between an outercasing and an outlet pipe, for example, as in an oil or gas well.Similar structural improvements are provided which render devices soused more readily adapted to their intended use and more readily handledin the field.

The present invention is an improvement upon the prior art devices ofthe types mentioned above. Significant to he achievement of the improvedresults is the structure of the closed loop gas-impervious tubular bodyof an elastomeric material which is preferably formed from an extrudedsection. It is characterized by a joint at the confronting ends of theextruded section which are brought into juxtaposed abutting relation toform the loop. The seal is designed so that such joint is subjected tosubstantial compressive stresses in the inflated condition as opposed totensile stresses. Therefore, the tendency for leakage to occur at thejoint is eliminated.

In one preferred embodiment of this invention, the extruded seal memberis provided with slots at its ends which are adapted to receive andretain a relatively short and relatively rigid member, e.g., a metallicinterlocking member. Such interlocking member bridges the outer portionof the joint and prevents any leakage along such portion. The force ofengagement along the remaining portions of the joint increase with sealinflation pressure so leakage does not occur. The abutting ends requireno adhesive, although an adhesive, particularly of the non-settingand/or pressure sensitive type, may be used if desired. With such astructure, installation or removal of a seal member can be readilyaccomplished without removal of the shaft, nor is it necessary that theseal housing be split, since the seal may be inserted and removed fromthe end of a solid one piece housing.

The seal is also designed for close fitting coaction with a recess in ashaft seal housing when embodied in a shaft seal structure for a marinepropeller shaft. For ready removability, the housing of the shaft sealstructure is provided with a removable retaining flange axiallyremovable from the shaft seal housing to permit access to theinflatable-peripheral seal.

When the inflatable peripheral seal of the present invention is adaptedfor sealing coaction with the internal surface of a tubular member, astructure is used which is similar in many respects to the shaft sealfor marine propeller shafts. However, the sealing surface is opposite tothat of the shaft seal structure as hereinafter more particularlydescribed.

The illustrated inflatable sealing of the present invention has aninternal peripheral cavity having at least one flexible wall removablebetween a first position and a second position in response to fluidpressure and which are stable in the first position when the pressuredifferential across the wall is below a predetermined positive value.The exterior surface of the flexible wall is, as indicated above, eitheran inner or an outer sealing surface, and is substantially free ofperipherally directed tensile stress in either position. The sealingsurface is adapted for sealing engagement with a confronting rigidsurface. In order to provide for pressurizing the deviceand causingmovement of the flexible wall into and out of sealing engagement with aconfronting rigid surface, there is provided an internal continuouschamber adapted to receive and contain fluid gas, usually air underpressure.

, Access to the internal chamber is provided by a rigid inlet duct orfitting which extends with an interference fit through a wall of theinflatable seal other than the flexible sealing wall. In a preferredembodiment the fitting provides a rigid tubular body which protrudesslightly beyond the associated wall into the internal fluid chamber. Theinitial seal is provided by the interference fit and the pressure of thefluid increases the sealing pressure as a direct function of fluidpressure so leakage does not occur.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary partially cutaway view of the stern portion of a marine vessel showing a marinepropeller shaft extending through the ships hull and provided with apropeller shaft seal structure embodying the improved inflatableperipheral seal of the present invention;

FIG. 2 is an enlarged ,view partially in section of the packing glandseal housing in accordance with this invention illustrating thestructural detail thereof;

FIG. 3 is an enlarged fragmentary section of the housing and sealillustrating the seal in the deflated condition;

FIG. 3a is an enlarged fragmentary view similar to FIG. 3 illustratingthe seal in the inflated and sealing condition;

FIG. 4 is an enlarged fragmentary view illustrating the cross section ofthe seal prior to installation thereof in the housing;

FIG. 5 is a fragmentary perspective view illustrating the bridging clipwhich extends between the ends of the seal;

FIG. 6 is a fragmentary section of a second embodiment'of a seal inaccordance with this invention illustrating such seal in the deflatedcondition; and

FIG. 7 is a fragmentary section of the seal illustrated in FIG. 6showing the seal in an inflated and operative position.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustratesthe stern portion of a typical marine propulsion system. A stern tube 10is supported at its outboard end by the hull structure 11 and itsforward end by a bulk head 12. A propulsion shaft 13 extends through thestern tube 10 and an outboard bearing 14 adjacent to a propulsion screw16. Water lubricated bearings of the type illustrated in our applicationfor US. Letters Patent, Ser. No. 653,796, Filed July 17, 1967, may beprovided in the stern tube 10 and the outboard bearing 14 to support theshaft 13 for rotation. Mounted on the inner end of the stern tube 10 isa seal assembly 17 which prevents flow of water along the shaft 13 intothe hull l1. Mounted in the seal assembly is a packing gland assemblyand an inflatable seal in accordance with the present invention.

Referring to FIG. 2, the seal assembly includes a main housing member 18provided with an inwardly extending shoulder 19. A packing assemblyconsisting of a plurality of packing rings 21 and a lantern ring 22 ispositioned within the housing member 18 inboard of the shoulder 19 andare adjustably compressed by a gland ring 23. The adjustment of thegland ring is provided by nuts 24 threaded onto bolts 26. A lubricantsuch as a petroleum grease is supplied through a fitting 27 to thelantern ring 22 which insures the even distribution of the lubricantaround the gland. In practice, the gland ring 23 is adjusted so that acontrolled relatively small amount of leakage occurs past the packingrings 21. With such adjustment, the water flowing past the packing ringscooperates with the petroleum lubricant to provide lubrication betweenthe shaft 13 and the packing rings and provides sufficient cooling toprevent excessive heat from being developed. As the packing rings wear,the gland ring 23 is tightened to maintain proper operation until thepacking is sufficiently worn to require replacement. Reference may bemade to our copending application, referred to above, for a moredetailed description of the function and operation of the packing glandassembly.

An inflatable seal 28 is mounted in the housing member 18 outboard ofthe should 19. The seal 28 extends between the shoulder 19 and aremovable shoulder or ring 29. The seal 28 when deflated, is spaced fromthe surface of the shaft 13 and when inflated, is pressed against theshaft 13 to provide a positive seal therewith. Fluid under pressure,usually air, is supplied to the seal through a fitting 31 to inflate theseal. Normally the housing member 18 is positioned against the inboardend of the stern tube 10, as illustrated in FIG. 1 and is retained inposition by bolts 32 which extend through bolt holes 33 in a flange 34.The flange 34 is illustrated in phantom in FIG. 2 in the normaloperative position.

When it is necessary to remove or replace a seal 28 the bolts 32 areremoved and the seal housing assembly 17 is moved along the shaft 13 asillustrated in FIG. 2 to provide access to the ring 29. The method ofinstallation and removal of the ring is discussed in detail below.

When the shaft isoperating lubricating water for the water lubricatedrubber bearing in the stern tube may be supplied to the bearing throughperipherally spaced openings 30 which extend through the shoulder 19.Water supplied through such opening flows along the shaft 13 past theseal 28 to the bearing within the stern tube.

Referring to FIGS. 3 through 5, the seal 28 is formed of an elongatedbody 36 of a gas-impervious elastomeric material, usually rubber. Thebody includes an outer peripheral wall 37 of relatively thick section,an inner peripheral and flexible wall 38 of thinner section, andradially extending end walls 39. A continuous internal chamber 41 isprovided within the seal 28. The body 28 is formed with axiallyextending flanges 45 which interwithin the chamber 41 exceeds thesurrounding pressure by less than a positive predetermined amount. Thisis accomplished by arranging the structure so that the flexible wall 38is in substantially its unstressed condition when it is concaved asillustrated in FIG. 3. In such condition, the seal is spaced from theshaft 13 and no wear can occur. When the chamber 41 is pressurized byadmitting fluid under pressure, such as air, through the fitting 31, thewall 38 snaps through to the position illustrated in FIG. 3a and engagesthe surface of the shaft 13 with sufficient pressure to prevent anyleakage along the shaft past the seal. Because the central portion ofthe flexible wall 38 moves radially inward during inflation, theperipheral length of the wall must reduce and the wall is placed in acompressive stress. Therefore, the wall does not move to the inflatedposition until sufficient pressure exists within the chamber 41 toovercome the compressive stress and cause the wall to move to its sealedand operative position.

The structure of the seal is also arranged so that the wall 38 isbistable. This results from the fact that the lateral width of the wall38 is constant due, in part, to the confinement provided by the housingso that the initial movement of the wall 38 from its position of FIG. 3produces lateral compression in the material forming the wall whichresists this movement. However, once the wall passes through an unstableposition in which the effect of the lateral compression forces in thewall reverse, these stresses tend to cause the wall to snap on throughthe inflated and sealed position of FIG. 3a. The position of instabilityis the position in which the wall is substantially straight, since thelateral width of the wall is smallest at this time and increases whenthe wall moves to either the concave release position or the convexinflated position.

When the chamber 41 is exhausted and the pressure therein decreases thisbistable characteristic of the wall tends to retain the wall 38 in theoperative position until the force of the fluid under pressure in thechamber 41 decreases to a value sufficiently low to cause theperipherally directed compressive stresses in the wall to overcome thelateral stresses and the pressure induced force. When this occurs, thewall 38 snaps back to its release condition. Preferably, the seal isarranged so that this occurs when the pressure in the chamber 41 isstill greater than the surrounding pressure by some positivepredetermined value in the order of at least 2 to 5 pounds. Therefore,when an operator releases the pressure in the chamber 41, the wall willsnap back to its release position even if the operator inadvertentlyleaves a material positive pressure within the chamber 41. Consequently,the tendency for the seal to be inadvertently left partially inflatedand in contact with the shaft 13, is substantially eliminated. Further,the structural arrangement wherein compressive stresses are created inthe wall 38 during inflation of sufficient magnitude to insure a snapaction to the release position, materially reduces the tendency for thematerials to take a sufficient set during inflation to cause a residualcontact to remain between the seal and the shaft.

In the illustrated embodiment, the wall 38 is formed with twoperipherally extending ribs 40 to provide an increase in thickness inthe center portion of the wall 38. With this structure, the amount ofmaterial subjected to compressive stress can be increased thusincreasing the magnitude of the compressive stress forces when inflatedwithout materially increasing the lateral stiffness of the wall. Theproper selection of the thickness of the wall 38 between the side walls39 and the ribs 40 provides the desired amount of snap action and theseparate selection of the size of the ribs provides the desired amountof force urging the wall to its concave position.

Although the operational advantages discussed above can be obtained witha one piece seal which has to be assembled over the end of a shafteither by sliding it along the shaft or by withdrawing the shaft fromthe housing while the seal is positioned, the preferred structure of aseal in accordance with this invention can be installed into a solidhousing without relative movement of the seal over the end of the shaft.Therefore, such seal can be installed or replaced without removing theshaft 13 from the housing 18 or moving the housing to the end of theshaft. In accordance with this aspect of the invention the seal isformed of an elongated body having ends which are joined after the sealis positioned around the shaft 13. Preferably, the body 36 is formed byextruding an elongated piece of elastomeric material in substantiallythe shape illustrated in FIG. 4. The body is then wrapped around amandrel to a circular shape with the two ends substantially abutting.While held in this ring shape the elastomeric material is cured and thebody is in the shape of a ring having two free ends of a mating shape.These two ends are the ends 43 and 44 illustrated in FIGS. 4 and 5.

Because the body 36 is formed of a flexible material the ends 43 and 44can be pulled apart and pulled up over the shaft 13 and reclosed withthe ring seal positioned around the shaft. The length of the ring issized so that it snugly fits into the recess in the housing member 18and the ends 43 and 44 are in abutting relationship at that time. Asmentioned previously, access to permit the removal or insertion of theseal is provided by removing the bolts 32 and sliding the seal housingassembly 17 along the shaft as illustrated in FIG. 2. When this is donethe ring 29 is removed by removing the screws 46 to provide access tothe seal proper. The ring 29 can be formed as a single continuous ringor can be formed as a group of segments which cooperate when the ring ismounted in place to form a ring extending completely around the shaft.Because the housing 18 and the ring 29 radially and axially confine theseal 28 with the ends 43 and 44 in abutment, pressurization of thechamber 41 does not produce any circumferentially directed tensilestress in the ring so the two end faces 43 and 44 are not pulled apart.Consequently, it is not necessary to provide a permanent bonded typeconnection between the two ends, although such a connection can be usedif desired.

Even when no connection is provided between the ends there is notendency for the seal to leak across the flexible wall 38 portion of thejoint since pressurization of the seal causes the wall 38 to be placedin circumferentially directed compressive stress, and such stress causesthe pressure of engagement between the ends of the wall 38 to increasewith pressure and maintain a nonleaking joint. If leakage tends tooccur, it will occur only across the portion of the joint along theouter wall 37 and the end walls 39. To prevent such leakage we provide asubstantially rigid bridging clip or member 47. This member ispreferably formed of sheet metal and has a U-shape with the base 48 ofthe U projecting into the outer wall. 37 and the legs 49 of the Uextending down along the end walls 39. Preferably, the ends of the body28 are formed with a slit or cut 51 proportioned to receive the bridgingmember 47 as illustrated in FIG. with the bridging member 47 extendingabout half of its length into one end and extendable through the otherhalf of its length into the other end.

Preferably, the bridging member 47 is installed and adhesively securedin one end of the seal at the time of manufacture, so that it will notbe lost during shipment. However, such adhesive connection is notnecessary for purposes of establishing a seal since once the ends arepushed together with the bridging member extending therebetween, theforce of the fluid under pressure in the chamber 41 increases thesealing pressure of engagement between the adjacent parts of the rubberand the bridging member. In practice, it has been found that a sealprovided with a bridging member in this manner can be pressurized andmaintains the pressure without leakage for extended periods of time eventhough the two ends 43 and 44 of the body 28 are not adhesivelyconnected and merely abut each other, and even though no positiveconnection is provided between the flexible wall portions 38 of the end.

The fittings 31 are preferably inserted after the seal 28 is positionedwithin the housing 18 and the ring 29 is installed. Since it would bevery difficult to orient the seal 28 in a predetermined position, thering 28 is installed with the fittings 31 removed. Removal of thefittings is accomplished merely by unscrewing them from the threadedopenings in the housing. While the fittings are removed and when theseal is in place, a hole 52 is cut through the outer wall 37 byinserting a cutter or drill through the opening 53 in he housing member18. Preferably, the cutter or drill should be substantially the samesize as the opening 53 since elastomeric material tends to spring backwhen out in this manner.

After the hole 52 is cut through the wall, the fitting 31 is threadedinto the body 18 so thatits tubular extension 54 extends through thehole 52 with an interference fit. Preferably, the tubular projection 54is lubricated so that it will slide through the hole 52 during theinsertion. Such lubrication can be obtained by merely wetting thetubular extension 54 since water provides a, good lubricant withrubber-like elastomeric material. The fitting is then connected througha tubular projection 56 to a valved source of fluid under pressure sothat the seal may be inflated and deflated.

It is important to arrange the structure so that the tubular projection54 extends slightly past the wall 37 as illustrated in FIGS. 3 and 4.This prevents the wall from hanging up on the end of the tubularprojection and allows the wall to compress inwardly against the tubularprojection as the chamber is pressurized. This maintains a sealingpressure along the interface which is greater than the pressure of thefluid being sealed. It is merely necessary to insert the seal so thatthe bridging clip 47 and the joint is spaced peripherally from thefitting 31.

Preferably the body 28 is molded so that the outer wall 37 is convex inits unstressed condition as illustrated in FIG. 4 and the mating cavityin the housing is provided with a cylindrical surface. Therefore, theinsertion of the seal radially deflects the outer wall 37 inward toinsure a tight engagement between the end faces along the outer wall andto insure a tight engage ment of the wall adjacent to the tubularextension 54.

FIGS. 6 and 7 illustrate a second embodiment of this invention in whichan inflatable seal is provided to seal with an internal cylindricalsurface. In this embodiment a ring seal 61 formed of an elastomericgas-impervious material is mounted on the outer surface of a cylindricalmember 62 between axially spaced shoulder elements 63. When deflated asillustrated in FIG. 6, the seal 61 is spaced from the inner surface 60of an outer cylindrical member 64 and when the seal is inflated the wallexpands out into engagement with the cylindrical member as illustratedin FIG. 7.

Here again the seal 61 is preferably formed of extruded materialproviding an inner wall 66, an outer flexible wall 67 and two side walls68. The seal provides an interior continuous chamber 69 through whichfluid under pressure may be admitted through a fitting 71 similar to thefitting discussed above in connection with the first embodiment.

In the second embodiment the seal is extruded with a shape substantiallyas illustrated in FIG. 7 so that the materials forming the flexible wall67 is substantially unstressed when the seal is inflated as illustratedin FIG. 7. The seal is provided with a tension ring 72 formed of elasticmaterial which is stretched around the outer wall 67 and compresses theouter wall inwardly to the deflected position of FIG. 6 when the chamber69 is not pressurized. This tension member may be formed of anelastomeric material such as rubber having a greater tensile strengththan the rubber forming the main body or may include other elasticmaterials of high tensile strength. In fact, the tension member may beformed of a high tensile strength rubber material provided withcircumferentially directed filaments 73 of high tensile strength such assuitable metal filaments or filaments formed of other materials.

When the chamber 69 is not pressurized, the wall 67 is deformed inwardlyand the seal is spaced from the inner surface 60 of the cylindricalmember 64. However when the chamber 69 is pressurized, sufficient radialforces are developed to stretch the tension member 72 and cause the sealto extend to the operated position of FIG. 7 in which the seal engagesthe cylindrical member 64 with sealing engagement. If the surface of thetensile member is of a type which does not provide good sealingengagement with the tubular member 64, the seal 61 can be formed withradially extending ribs 74 which tightly engage the member 64 to providea proper seal. In FIG. 7 such ribs have been elastically deformed by theengagement.

Because the wall 67 is molded initially to have a shape substantiallythe same as the shape it assumes in the inflated and sealed condition,it is not subjected to any significant peripherally directed tensilestresses. Therefore, the joint between the ends of the seal are notsubjected to any destructive forces which would tend to cause jointfailure. In most instances, however, the seal of this second embodimentis formed with a permanent bonded type joint at the ends of the body toinsure that the fluid in the chamber 69 cannot leak out through theflexible wall 67 at the area of the joint. Such joint, however, sinceitis not subjected to damaging tensile stresses, is not damaged in theuse of the device. The material forming the tension member should be atype which does not take a permanent set when subjected to tensilestresses so that the seal will return to its deflated and releasedcondition when the pressure in the chamber 69 is relieved.

Although preferred embodiments of this invention are illustrated, it isto be understood that various modifications and rearrangements of partsmay be resorted to without departing from the scope of the inventiondisclosed.

What is claimed is:

1. An inflatable annular seal comprising a closed loop having oppositelydisposed peripheral sealing surfaces, said loop including a body ofgas-impervious elastomeric material formed with an internal chamber,said body providing at least one flexible wall means movable betweenfirst and second positions in response to changes in fluid pressurewithin said chamber for causing at least one of said sealing surfaces tomove between operative and inoperative positions, said wall meansremaining substantially in said first position with said one sealingsurface substantially spaced from its operative position when thepressure in said chamber exceeds the pressure on the exterior of saidseal by less than a predetermined positive differential pressure andmoving to said second position causing said one sealing surface to moveto its operative position only when such differential pressure exceedssaid predetermined differential pressure, said internal chamber beingcontinuous, said body being formed with an elongated section joined atits ends, and said wall means being free of peripherally directedtensile stresses when said wall is in either of said positions, saidwall means being concave in one of said positions and being convex inthe other of said positions.

2. An inflatable annular seal as set forth in claim 1 wherein said wallmeans has longitudinally extending sides, and means are provided tomaintain a substantially constant spacing between said sides.

3. An inflatable seal comprising a closed loop having oppositelydisposed peripheral sealing surfaces, said loop including a body ofgas-impervious elastomeric material formed with an internal chamber,said body providing at least one flexible wall means movable betweenfirst and second positions in response to changes in fluid pressurewithin said chamber for causing at least one of said sealing surfaces tomove between operative'and inoperative positions, said wall meansremaining substantially in said first position with said one sealingsurface substantially spaced from its operative position when thepressure in said chamber exceeds the pressure on the exterior of saidseal by less than a predetermined positive differential pressure andmoving to said second position causing said one sealing surface to moveto its operative position only when such differential pressure exceedssaid predetermined differential pressure, said wall means being providedwith at least one peripherally extending integrally formed rib withinsaid internal chamber which operates to resist movement of said wallmeans from said first position to said second position.

4. An inflatable annular seal as set forth in claim 3 wherein saidinternal chamber is continuous, said wall means is the inner wall ofsaid loop and the material faces, said loop including a body ofgas-impervious elastomeric material formed with a continuous internalchamber, said body providing at least one flexible wall movable betweenfirst and second positions in response to changes in fluid pressurewithin said chamber for causing at least one of said sealing surfaces tomove between operative and inoperative positions, said wall remainingsubstantially in said first position when the pressure in said chamberexceeds the pressure on the exterior of said seal by less than apredetermined positive differential pressure and moving to said secondposition only when such differential pressure exceeds said predetermineddifferential pressure, said wall being provided with at least oneperipherally extending integrally formed rib which operates to resistmovement of said wall from said first position to said second position,said wall being the inner wall of said loop and the material formingsaid wall and rib are subject to increased compressive stress as saidwall moves from said first position to said second position, saidmaterial of said wall being substantially free of stresses when saidwall is in said first position, said body includes at least oneelongated member of substantially uniform cross section with at leastone of its ends joined to an adjacent similar end, and a bridgingelement extends between said ends and provides a seal jointtherebetween.

7. An inflatable annular seal as set forth in claim 6 wherein saidbridging element is a substantially rigid element embedded into thematerial of each of said ends.

8. An inflatable annular seal as set forth in claim 7 wherein saidbridging element is U-shaped and connects said ends excepting along saidflexible wall.

9. An inflatable annular seal as set forth in claim 8 wherein saidbridging element provides the only positive connection between saidends.

10. An inflatable annular seal as set forth in claim 9 wherein said bodyis a one piece extruded member joined at its ends.

11. An inflatable seal comprising a closed loop having oppositelydisposed peripheral sealing surfaces, said loop including a body ofgas-impervious elastomeric material formed with an internal chamber,said body providing at least one flexible wall means movable betweenfirst and second positions in response to changes in fluid pressurewithin said chamber for causing at least one of said sealing surfaces tomove between operative and inoperative positions, said wall meansremaining substantially in said first position with said one sealingsurface substantially spaced from its operative position when thepressure in said chamber exceeds the pressure on the exterior of saidseal by less than a predetermined positive differential pressure andmoving to said second position causing said one sealing surface to moveto its operative position only when such differential pressure exceedssaid predetermined differential pressure, said seal including a memberresiliently urging said wall toward said first position and placing thematerial of said wall in compression when said wall is in said firstposition.

12. An inflatable annular seal as set forth in claim 1 1 wherein saidmember is in tension and is formed of elastic material extending alongthe outer peripheral surface of said loop, and said wall is adjacent tosaid member.

13. An inflatable annular seal as set forth in claim 12 wherein saidbody is substantially free of tensile stresses in both of said first andsecond positions.

14. A shaft seal comprising in combination a housing assembly providinga pair of opposed axially spaced radially extending shoulderscooperating with an axially extending wall to define an annular groove,a shaft extending past said groove, an inflatable closed loop seal insaid groove around said shaft, said seal including a body ofgas-impervious elastomeric material formed with an internal chamber,said body providing at least one flexible wall means movable between afirst position spaced from said shaft and a second position in sealingengagement with said shaft, said wall means remaining substantially insaid first position when the pressure in said chamber exceeds thepressure on the exterior of said seal by less than a predeterminedpositive differential pressure and moving to said second position onlywhen said differential pressure exceeds said predetermined differentialpressure, said wall means moving said second position to said firstposition when the pressure in said chamber exceeds the pressure exteriorof said seal by a predetermined positive value, said internal chamberbeing continuous, said loop being formed of an elongated body of uniformcross section provided with a joint at its ends, said ends being joinedafter said seal is positioned around said shaft, said body beingsubstantially free of tensile stresses when said wall means is in eitherof said positions, one of said shoulders being removable to permitinstallation and removal of said seal without removing said shaft, saidwall means being concave when in said first position and being convexwhen in said second position.

15. A shaft seal as set forth in claim 14 wherein said shaft is apropeller shaft of a marine vessel, and said seal prevents flow of wateralong said shaft when said wall means is in said second position.

16. A shaft seal as set forth in claim 15 wherein said shaft extendsinto said vessel through a stern tube, said housing assembly includes apacking gland inboard of said seal, and said housing is releasablyconnected in sealing engagement with said stern tube.

17. A shaft seal as set forth in claim 16 wherein said housing ismovable along said shaft away from said stern tube to provide access tosaid one of said shoulders.

18. A shaft seal as set forth in claim 14 wherein said housing assemblyprovides a fitting having a tubular extension extending through a wallof said seal other than said flexible wall means into said chamber.

19. A shaft seal as set forth in claim 18 wherein said fitting isremovable and said seal resiliently engages the exterior of said tubularprojection at a location spaced from its inner end.

20. An inflatable annular seal comprising a closed loop havingoppositely disposed peripheral sealing surfaces, said loop including abody of gas-impervious elastomeric material formed with a continuousinternal chamber, said body providing at least one flexible wall movablebetween first and second positions in response to changes in fluidpressure within said chamber for causing at least one of said sealingsurfaces to move between operative and inoperative positions, said wallremaining substantially in said first position when the pressure in saidchamber exceeds the pressure on the stantially uniform cross sectionwith at least one of its ends joined to an adjacent similar end, and abridging element extends between said ends and provides a seal jointtherebetween.

1. An inflatable annular seal comprising a closed loop having oppositelydisposed peripheral sealing surfaces, said loop including a body ofgas-impervious elastomeric material formed with an internal chamber,said body providing at least one flexible wall means movable betweenfirst and second positions in response to changes in fluid pressurewithin said chamber for causing at least one of said sealing surfaces tomove between operative and inoperative positions, said wall meansremaining substantially in said first position with said one sealingsurface substantially spaced from its operative position when thepressure in said chamber exceeds the pressure on the exterior of saidseal by less than a predetermined positive differential pressure andmoving to said second position causing said one sealing surface to moveto its operative position only when such differential pressure exceedssaid predetermined differential pressure, said internal chamber beingcontinuous, said body being formed with an elongated section joined atits ends, and said wall means being free of peripherally directedtensile stresses when said wall is in either of said positions, saidwall means being concave in one of said positions and being convex inthe other of said positions.
 2. An inflatable annular seal as set forthin claim 1 wherein said wall means has longitudinally extending sides,and means are provided to maintain a substantially constant spacingbetween said sides.
 3. An inflatable seal comprising a closed loophaving oppositely disposed peripheral sealing surfaces, said loopincluding a body of gas-impervious elastomeric material formed with aninternal chamber, said body providing at least one flexible wall meansmovable between first and second positions in response to changes influid pressure within said chamber for causing at least one of saidsealing surfaces to move between operative and inoperative positions,said wall means remaining substantially in said first position with saidone sealing surface substantially spaced from its operative positionwhen the pressure in said chamber exceeds the pressure on the exteriorof said seal by less than a predetermined positive differential pressureand moving to said second position causing said one sealing surface tomove to its operative position only when such differential pressureexceeds said predetermined differential pressure, said wall means beingprovided with at least one peripherally extending integrally formed ribwithin said internal chamber which operates to resist movement of saidwall means from said first position to said second position.
 4. Aninflatable annular seal as set forth in claim 3 wherein said internalchamber is continuous, said wall means is the inner wall of said loopand the material forming said wall means and rib are subjected toincreased compressive stress as said wall means moves from said firstposition to said second position.
 5. An inflatable annular seal as setforth in claim 4 wherein said material of said wall means issubstantially free of stresses when said wall is in said first position.6. An inflatable annular seal comprising a closed loop having oppositelydisposed peripheral sealing surfaces, said loop including a body ofgas-impervious elastomeric material formed with a continuous internalchamber, said body providing at least one flexible wall movable betweenfirst and second positions in response to changes in fluid pressurewithin said chamber for causing at least one of said sealing surfaces tomove between operative and inoperative positions, said wall remainingsubstanTially in said first position when the pressure in said chamberexceeds the pressure on the exterior of said seal by less than apredetermined positive differential pressure and moving to said secondposition only when such differential pressure exceeds said predetermineddifferential pressure, said wall being provided with at least oneperipherally extending integrally formed rib which operates to resistmovement of said wall from said first position to said second position,said wall being the inner wall of said loop and the material formingsaid wall and rib are subject to increased compressive stress as saidwall moves from said first position to said second position, saidmaterial of said wall being substantially free of stresses when saidwall is in said first position, said body includes at least oneelongated member of substantially uniform cross section with at leastone of its ends joined to an adjacent similar end, and a bridgingelement extends between said ends and provides a seal jointtherebetween.
 7. An inflatable annular seal as set forth in claim 6wherein said bridging element is a substantially rigid element embeddedinto the material of each of said ends.
 8. An inflatable annular seal asset forth in claim 7 wherein said bridging element is U-shaped andconnects said ends excepting along said flexible wall.
 9. An inflatableannular seal as set forth in claim 8 wherein said bridging elementprovides the only positive connection between said ends.
 10. Aninflatable annular seal as set forth in claim 9 wherein said body is aone piece extruded member joined at its ends.
 11. An inflatable sealcomprising a closed loop having oppositely disposed peripheral sealingsurfaces, said loop including a body of gas-impervious elastomericmaterial formed with an internal chamber, said body providing at leastone flexible wall means movable between first and second positions inresponse to changes in fluid pressure within said chamber for causing atleast one of said sealing surfaces to move between operative andinoperative positions, said wall means remaining substantially in saidfirst position with said one sealing surface substantially spaced fromits operative position when the pressure in said chamber exceeds thepressure on the exterior of said seal by less than a predeterminedpositive differential pressure and moving to said second positioncausing said one sealing surface to move to its operative position onlywhen such differential pressure exceeds said predetermined differentialpressure, said seal including a member resiliently urging said walltoward said first position and placing the material of said wall incompression when said wall is in said first position.
 12. An inflatableannular seal as set forth in claim 11 wherein said member is in tensionand is formed of elastic material extending along the outer peripheralsurface of said loop, and said wall is adjacent to said member.
 13. Aninflatable annular seal as set forth in claim 12 wherein said body issubstantially free of tensile stresses in both of said first and secondpositions.
 14. A shaft seal comprising in combination a housing assemblyproviding a pair of opposed axially spaced radially extending shoulderscooperating with an axially extending wall to define an annular groove,a shaft extending past said groove, an inflatable closed loop seal insaid groove around said shaft, said seal including a body ofgas-impervious elastomeric material formed with an internal chamber,said body providing at least one flexible wall means movable between afirst position spaced from said shaft and a second position in sealingengagement with said shaft, said wall means remaining substantially insaid first position when the pressure in said chamber exceeds thepressure on the exterior of said seal by less than a predeterminedpositive differential pressure and moving to said second position onlywhen said differential pressure exceeds said predetermined differentialprEssure, said wall means moving said second position to said firstposition when the pressure in said chamber exceeds the pressure exteriorof said seal by a predetermined positive value, said internal chamberbeing continuous, said loop being formed of an elongated body of uniformcross section provided with a joint at its ends, said ends being joinedafter said seal is positioned around said shaft, said body beingsubstantially free of tensile stresses when said wall means is in eitherof said positions, one of said shoulders being removable to permitinstallation and removal of said seal without removing said shaft, saidwall means being concave when in said first position and being convexwhen in said second position.
 15. A shaft seal as set forth in claim 14wherein said shaft is a propeller shaft of a marine vessel, and saidseal prevents flow of water along said shaft when said wall means is insaid second position.
 16. A shaft seal as set forth in claim 15 whereinsaid shaft extends into said vessel through a stern tube, said housingassembly includes a packing gland inboard of said seal, and said housingis releasably connected in sealing engagement with said stern tube. 17.A shaft seal as set forth in claim 16 wherein said housing is movablealong said shaft away from said stern tube to provide access to said oneof said shoulders.
 18. A shaft seal as set forth in claim 14 whereinsaid housing assembly provides a fitting having a tubular extensionextending through a wall of said seal other than said flexible wallmeans into said chamber.
 19. A shaft seal as set forth in claim 18wherein said fitting is removable and said seal resiliently engages theexterior of said tubular projection at a location spaced from its innerend.
 20. An inflatable annular seal comprising a closed loop havingoppositely disposed peripheral sealing surfaces, said loop including abody of gas-impervious elastomeric material formed with a continuousinternal chamber, said body providing at least one flexible wall movablebetween first and second positions in response to changes in fluidpressure within said chamber for causing at least one of said sealingsurfaces to move between operative and inoperative positions, said wallremaining substantially in said first position when the pressure in saidchamber exceeds the pressure on the exterior of said seal by less than apredetermined positive differential pressure and moving to said secondposition only when such differential pressure exceeds said predetermineddifferential pressure, said body being formed of at least one elongatedmember of substantially uniform cross section with at least one of itsends joined to an adjacent similar end, and a bridging element extendsbetween said ends and provides a seal joint therebetween.